Alexander Sotkin may have thought he was harmlessly posting selfies to his friends back home, but last night the 24-year-old Russian soldier was at the centre of international intrigue.

For the photographs he has posted on the web appear to offer evidence that Vladimir Putin’s forces have been operating inside Ukraine.

Geotagging – the process of adding a location to a photograph taken by a mobile phone camera – creates a trail that leads Sotkin, a sergeant in the signals corps, from a military base in southern Russia across the troublesome border to villages inside rebel-held parts of Ukraine. . .